The present invention relates to a thermal transfer recording apparatus and, more particularly, to a thermal transfer recording apparatus which allows a thermal head to press on a platen roller, through ink and printing sheets interposed in between, with increased intensity by means of a simple mechanism and, yet, enhances fast movements of the thermal head into and out of the vicinity of the platen roller.
As well known in the art, thermal transfer recording is effected by causing an ink sheet which is provided with an ink layer on one surface thereof and a recording sheet into contact, then pressing a thermal head against the other surface of the ink sheet, and then applying a current to selected ones of heating resistors of the thermal head to heat the head. The heat of the head melts the ink on the ink sheet to transfer it to the recording sheet.
A prior art apparatus for such thermal transfer recording includes a platen roller, a thermal head, a support plate adapted to support the thermal head at one end thereof and pivotally movable about a fulcrum to bring the head into and out of the vicinity of the platen roller, and a pull-type solenoid device having a plunger, a drive shaft, which is connected to the other end of the support plate and directly reciprocated to move the support plate in the above-mentioned manner. The head is brought into the vicinity of the platen roller by the pull-type solenoid device and driven away from the platen roller by a spring.
As described above, movements of the head into and out of pressing contact with the platen roller with the sheets interposed in between have customarily been implemented with the pull-type solenoid mounted on one end of the head support plate, which is movable in a seesaw motion, and the spring. The problem with this prior art apparatus is that when the solenoid device is actuated to press the head against the platen roller, the spring counteracts the solenoid device. Specifically, the head fails to press on the platen roller with sufficient pressure (which should generally to about 10 kilograms) unless the support plate is dimensioned longer between the fulcrum and the head than between the fulcrum and the drive shaft of the solenoid device or a large-scale pull-type solenoid device is used. This makes the whole apparatus bulky and aggravates power consumption.
Another problem with the prior art apparatus is that since the release of the head from the platen roller is effected by the spring which is anchored to the support plate, a substantial period of time is necessary for the head from being moved clear of the platen roller after the solenoid device is deenergized, that is, rapid release of the head is unattainable. In addition, such a slow escapement of the head away from the platen roller increases a chance of head collision with the platen roller at its protruding paper cramp.